Power reduction grid connection method and control system of wind generating set

Abstract

The invention belongs to the technical field of wind power generation, and relates to a power reduction grid connection method and control system of a wind generating set, the method is applied to the control system of the wind generating set, and comprises the following steps: monitoring the wind speed in real time, calculating the output power of the wind generating set when the wind speed continuously meets the running wind speed of the wind generating set in a preset time period, judging the magnitude of the output power and a preset power threshold value; if the output power is larger than the preset power threshold value, the paddle opening angle of paddles is controlled based on the current wind speed, and therefore the rotating speed of a motor is adjusted and controlled; when the rotating speed of the motor reaches the synchronous speed interval range, the motor is controlled to be switched on and connected; based on the real-time operation state parameters of the wind generating set, the real-time state parameters of the user side and the real-time state parameters of the power grid side, the grid-connected state of the wind generating set is judged, and when the grid-connected fault of the wind generating set occurs, a motor is controlled By means of the grid connection method, safe and stable grid connection of the wind generating set can be controlled.

Description

Technical Field

[0001] The present invention relates to the technical field of wind power generation, and in particular to a method and control system for reducing the power of a wind turbine generator set to be connected to the grid. Background Art

[0002] The electric energy generated by a wind turbine generator set needs to be connected to the grid through grid connection in order to transmit the electric energy to the user side to meet the user's power consumption requirements. Since the wind speed is the power source of wind power generation, but the wind speed is random and intermittent, it is difficult to accurately predict and control, which leads to frequent and large fluctuations in the output power of the wind turbine generator set, making it difficult to ensure the smoothness and stability of the output power during grid connection. Therefore, how to control the safe and stable grid connection of the wind turbine generator set is an urgent problem to be solved at present.

[0003] In the prior art, a wind turbine generator set based on an asynchronous motor usually adopts a direct grid connection method. However, at the moment when the asynchronous motor is connected to the grid, due to the differences in voltage and frequency between the motor and the grid, a large impact current will be generated, resulting in an instantaneous drop in the grid voltage and affecting the normal operation of other equipment in the grid. At the same time, after the motor is connected to the grid, its speed will be quickly pulled into synchronization by the grid frequency, absorbing a large amount of reactive power, resulting in voltage fluctuations or even instability in the grid. In addition, after the wind turbine generator set is connected to the grid, problems such as voltage instability and power oscillation will also occur, which will also affect the safe operation of the grid and the wind turbine generator set.

[0004] In summary, it is necessary to design a method that can control the safe and stable grid connection of the wind turbine generator set, effectively reduce the impact of the current impact during the grid connection process on the grid, and at the same time be able to detect grid connection problems after grid connection to control the wind turbine generator set to disconnect from the grid in time. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is to overcome the problem that the grid connection method of the wind turbine generator set in the prior art will bring an impact to the grid and cannot ensure the safe and stable operation of the grid and the wind turbine generator set before and after grid connection.

[0006] To solve the above technical problem, the present invention provides a method for reducing the power of a wind turbine generator set to be connected to the grid, which is applied to the control system of the wind turbine generator set and includes: Real-time monitoring of the wind speed. When the wind speed continuously meets the operating wind speed of the wind turbine generator set within a preset time period, calculate the output power of the wind turbine generator set, and judge the magnitude of the output power and a preset power threshold; If the output power is greater than the preset power threshold, control the opening angle of the blade based on the current wind speed, thereby regulating the motor speed; when the motor speed reaches the synchronous speed range, control the motor to switch on and connect to the grid; Based on the real-time operating state parameters of the wind turbine generator set, the real-time state parameters of the user side, and the real-time state parameters of the grid side, judge the grid connection state of the wind turbine generator set, and control the motor to trip and disconnect from the grid when a grid connection fault occurs in the wind turbine generator set.

[0007] Preferably, based on the real-time operating state parameters of the wind turbine generator set, the real-time state parameters of the user side, and the real-time state parameters of the grid side, judging the grid connection state of the wind turbine generator set and controlling the motor to trip and disconnect from the grid when a grid connection fault occurs in the wind turbine generator set includes: Obtain the real-time output power of the wind turbine generator set, the real-time power consumption of the user side, and the real-time output power of the grid side, and calculate the sum value of the real-time output power of the wind turbine generator set and the real-time output power of the grid side; If the sum value is not equal to the real-time power consumption of the user side, it is determined that there is a grid connection fault in the wind turbine generator set, and the motor is controlled to trip and disconnect from the grid.

[0008] Preferably, based on the real-time operating state parameters of the wind turbine generator set, the real-time state parameters of the user side, and the real-time state parameters of the grid side, judging the grid connection state of the wind turbine generator set and controlling the motor to trip and disconnect from the grid when a grid connection fault occurs in the wind turbine generator set includes: Judge whether the real-time output power of the wind turbine generator set is greater than the set ratio of the real-time power consumption of the user side; If the real-time output power of the wind turbine generator set is greater than the set ratio of the real-time power consumption of the user side, it is determined that there is a grid connection fault in the wind turbine generator set, and the motor is controlled to trip and disconnect from the grid.

[0009] Preferably, when the wind speed is less than or equal to 11 m / s, the set ratio is 80%; When the wind speed is greater than 11 m / s and less than 13 m / s, the set ratio is 70%.

[0010] Preferably, after controlling the motor to trip and disconnect from the grid, it further includes: reducing the opening angle of the blade to regulate the motor speed, and when the motor speed reaches the synchronous speed range again, controlling the motor to switch on and connect to the grid.

[0011] Preferably, reducing the opening angle of the blade includes: controlling the opening angle of the blade to decrease uniformly at a fixed change amount until the motor speed reaches the synchronous speed range.

[0012] Preferably, reducing the opening angle of the blade includes: Based on the opening angle of the blade and the motor speed at different wind speeds, construct a change curve graph of the motor speed with the opening angle of the blade at different wind speeds; Based on the change curve graph of the motor speed with the opening angle of the blade corresponding to the current wind speed, obtain the target opening angle of the blade corresponding to the synchronous speed range; Based on the blade's initial pitch angle and the target initial pitch angle, set the change amount of the initial pitch angle, and control the blade's initial pitch angle to decrease by the change amount of the initial pitch angle until the motor speed reaches the synchronous speed range.

[0013] Preferably, the preset time period is 10 min to 15 min; and / or The operating wind speed of the wind turbine generator set is 4 m / s to 25 m / s; and / or The preset power threshold is 10 Kw; and / or The synchronous speed range is 1490 r / min to 1510 r / min.

[0014] Preferably, controlling the blade's initial pitch angle based on the current wind speed includes: When the wind speed is greater than or equal to 4 m / s and less than or equal to 5 m / s, control the blade's initial pitch angle to be greater than 45° and less than 90°; When the wind speed is greater than 5 m / s and less than or equal to 8 m / s, control the blade's initial pitch angle to be less than 45°.

[0015] The present invention also provides a control system, and the control system is used to implement the steps of the above-mentioned method for reducing the power of the wind turbine generator set to connect to the grid.

[0016] The method for reducing the power of the wind turbine generator set provided by the present application first detects whether the wind speed continuously meets the operating wind speed of the wind turbine generator set within a period of time, so as to ensure that the wind speed can drag the wind turbine generator set to the rotational speed for connecting to the grid; then calculates the output power of the wind turbine generator set. When the output power of the wind turbine generator set reaches the preset power threshold, it indicates that the wind force is relatively stable and reaches a certain intensity. Therefore, when this condition is met, controlling the pitch angle of the blade according to the wind speed can more accurately control the motor speed; at the same time, when the motor speed reaches the synchronous speed range, the rotating magnetic field generated by its stator winding is more likely to match the rotating magnetic field of the grid in terms of frequency and phase, and the frequency of the alternating current output by it is also basically the same as the grid frequency, so as to reduce the current impact and electromagnetic force impact generated during the closing moment, ensure the stable operation of the grid and the wind turbine generator set, and can also enable the wind turbine generator set to quickly and smoothly follow the operating state of the grid after grid connection, improving the synchronization and coordination between the wind turbine generator set and the grid; after grid connection, the present application also judges the grid connection state of the wind turbine generator set by real-time monitoring the operating state parameters of the wind turbine generator set, the grid side and the user side, so as to timely detect problems such as voltage abnormalities, frequency fluctuations and power imbalance during the grid connection operation process, so that when a grid connection fault is found, the motor can be controlled to trip and disconnect from the grid in time, which not only ensures the safe and stable grid connection of the wind turbine generator set, but also can diagnose the fault and disconnect from the grid in time after grid connection, so that both the grid and the wind turbine generator set can operate safely and stably before and after grid connection. Description of the Drawings

[0017] To make the content of the present invention easier to be clearly understood, the following further details the present invention according to specific embodiments of the present invention in conjunction with the accompanying drawings, where: Figure 1 It is a schematic diagram of the power reduction grid connection principle of the wind turbine provided by this application; Figure 2 It is a flowchart of the power reduction grid connection method of the wind turbine provided by this application; Figure 3 It is a schematic diagram of the control system provided by this application. Specific Embodiments

[0018] The following further illustrates the present invention in conjunction with the accompanying drawings and specific embodiments, so that those skilled in the art can better understand the present invention and be able to implement it, but the illustrated embodiments are not used as a limitation to the present invention.

[0019] Please refer to Figure 1 , Figure 1 As shown, it is a schematic diagram of the power reduction grid connection principle of the wind turbine provided by this application. In the figure, Table 1 is used to detect the operating state parameters of the wind turbine, Table 2 is used to detect the user-side state parameters, and Table 3 is used to detect the grid-side state parameters. Since wind power generation cannot feed power back to the grid under the condition of self-use by users, an anti-counterflow device is set between the grid connection point and the grid side.

[0020] Figure 2 As shown, it is a flowchart of the power reduction grid connection method of the wind turbine provided by this application. This method is applied to the control system of the wind turbine and specifically includes: S10: Monitor the wind speed in real time. When the wind speed continuously meets the operating wind speed of the wind turbine within a preset time period, calculate the output power of the wind turbine and judge the magnitude relationship between the output power and the preset power threshold.

[0021] Further, the preset time period is 10 min to 15 min, the operating wind speed of the wind turbine is 4 m / s to 25 m / s, and the preset power threshold is 10 Kw.

[0022] S20: If the output power is greater than the preset power threshold, control the blade opening angle based on the current wind speed, thereby regulating the motor speed; when the motor speed reaches the synchronous speed range, control the motor to switch on and connect to the grid.

[0023] Further, the synchronous speed range is 1490 r / min to 1510 r / min. For example: when the control system detects that the motor speed is 1490 r / min, 1495 r / min, 1500 r / min, 1505 r / min or 1510 r / min, it can control the motor to switch on.

[0024] Specifically, when the motor speed is near the synchronous speed, the rotating magnetic field generated by its stator winding is more likely to reach a matching state with the rotating magnetic field of the power grid in terms of frequency and phase, and the frequency of the alternating current output by it is also basically the same as the power grid frequency, thereby reducing the current impact and electromagnetic force impact generated during the closing instant and ensuring the stable operation of the power grid and the wind turbine generator set. Once the motor speed deviates from the synchronous speed range, the phase difference and frequency difference between the motor and the power grid will start to increase, affecting grid connection. Based on this, in some embodiments of the present application, a sensitive detector is used to detect the motor speed in real time, so as to ensure that the seizure control closing is achieved when the motor speed reaches the synchronous speed range.

[0025] S30: Based on the real-time operating state parameters of the wind turbine generator set, the real-time state parameters of the user side, and the real-time state parameters of the power grid side, determine the grid connection state of the wind turbine generator set, and control the motor to trip and disconnect from the grid when a grid connection fault occurs in the wind turbine generator set.

[0026] Since the wind speed is too small to drag the wind turbine generator set to the speed for grid connection, the wind turbine is in a free rotation state, that is, a standby state. At this time, although the motor has not been connected to the power grid yet, the wind turbine generator set is in a working state; when the wind speed continuously meets the operating wind speed of the wind turbine generator set for a period of time, it indicates that the wind speed at this time can drag the wind turbine generator set to the speed for grid connection, and the control system starts to control the motor to be connected to the grid.

[0027] Specifically, since it is necessary to ensure that both the power grid and the wind turbine generator set are in a stable working state before the motor is connected to the grid, therefore, in some embodiments of the present application, when the wind speed continuously meets the operating wind speed of the wind turbine generator set within a preset time period, the control system also needs to detect whether the operating state parameters of the power grid and the wind turbine generator set are normal.

[0028] Exemplarily, when there are no overvoltage and low voltage in the power grid voltage within 10 consecutive minutes, the voltage drop value within 0.1 s is less than the set value, the power grid frequency is within the set range and there are no faults such as three-phase imbalance, etc., it indicates that the power grid is in a stable working state at this time. When the generator temperature and the speed increaser oil temperature of the wind turbine generator set are within the set range, the hydraulic system pressure is at the set value, the hydraulic oil level and the gear lubricating oil level are normal, the brake friction pads are normal, the power supplies of each control system are normal, and the maintenance switch is in the operating position, it indicates that the wind turbine generator set is in a stable working state at this time.

[0029] Furthermore, when the output power of the wind turbine generator set reaches the preset power threshold, it indicates that the wind force is relatively stable and reaches a certain intensity. At this time, by adjusting the opening angle of the paddle to control the motor speed, the motor speed can be more accurately controlled within the synchronous speed range, thereby completing the grid connection of the wind turbine generator set.

[0030] Further, in some embodiments of the present application, controlling the opening angle of the blade based on the current wind speed includes: When the wind speed is greater than or equal to 4 m / s and less than or equal to 5 m / s, control the opening angle of the blade to be greater than 45° and less than 90°; When the wind speed is greater than 5 m / s and less than or equal to 8 m / s, control the opening angle of the blade to be less than 45°.

[0031] Specifically, when the wind speed is between 4 m / s and 5 m / s, due to the low wind speed, in order to capture as much wind energy as possible, it is necessary to increase the contact area and angle between the blade and the air flow, so that the blade can more effectively utilize the wind energy to generate torque, thereby driving the motor to rotate; when the wind speed is between 5 m / s and 8 m / s, due to the relatively high wind speed, if the opening angle of the blade is still large, the aerodynamic force it bears will also be too large. Therefore, by adjusting the opening angle of the blade to below 45°, the blade can maintain a proper receiving state, and at the same time control the growth rate of the output power of the wind power generation set.

[0032] Further, after the wind power generation set is connected to the grid, it is necessary to monitor the state parameters of the grid side, the user side and the wind power generation set in real time, so as to disconnect from the grid in time when a grid connection operation failure is detected.

[0033] Specifically, in some embodiments of the present application, after the wind power generation set is successfully connected to the grid, it further includes: Obtain the real-time output power of the wind power generation set, the real-time power consumption of the user side and the real-time output power of the grid side, and calculate the sum value of the real-time output power of the wind power generation set and the real-time output power of the grid side; If the sum value is not equal to the real-time power consumption of the user side, it is determined that there is a grid connection failure of the wind power generation set, and the motor is controlled to trip and disconnect from the grid.

[0034] Exemplarily, as Figure 1 shown, when the sum value of the output power value detected in Table 1 and the output power value detected in Table 3 is equal to the power consumption value detected in Table 2, it indicates that the output power of the wind power generation set and the grid side can meet the power consumption of the user side at this time, and the supply and demand are matched at the power level, and there is no situation of power surplus or shortage.

[0035] Optionally, in some other embodiments, after the wind power generation set is successfully connected to the grid, it further includes: Judge whether the real-time output power of the wind power generation set is greater than the set ratio of the real-time power consumption of the user side; If the real-time output power of the wind power generation set is greater than the set ratio of the real-time power consumption of the user side, it is determined that there is a grid connection failure of the wind power generation set, and the motor is controlled to trip and disconnect from the grid.

[0036] Specifically, when the wind speed is less than or equal to 11 m / s, the set ratio is 80%; when the wind speed is greater than 11 m / s and less than 13 m / s, the set ratio is 70%. This is because when the wind speed is relatively low, the output power of the wind turbine is relatively low and the growth is relatively slow. As long as its output power does not exceed 80% of the user-side power consumption, it will not cause an impact on the power grid. It can not only supplement power to the power grid at low wind speeds, but also reserve a certain margin to cope with power fluctuations. When the wind speed is greater than 11 m / s, the output power of the wind turbine rises rapidly with the increase of the wind speed and the change is relatively drastic. When the output power of the wind turbine exceeds 70% of the user-side power consumption, tripping and disconnecting from the grid in time can prevent the output power of the wind turbine from approaching or exceeding the tolerance of the power grid and the user side too quickly, resulting in fluctuations in parameters such as the grid voltage and frequency, and further affecting the stable operation of the power grid.

[0037] Further, after the motor trips and disconnects from the grid, the motor speed is regulated by controlling the opening angle of the blade again, so as to control the wind turbine to reconnect to the grid.

[0038] Specifically, after controlling the motor to trip and disconnect from the grid, it also includes: reducing the opening angle of the blade to regulate the motor speed. When the motor speed reaches the synchronous speed range again, control the motor to switch on and connect to the grid.

[0039] Optionally, in some embodiments of the present application, the opening angle of the blade can be reduced quantitatively. Specifically, control the opening angle of the blade to decrease uniformly at a fixed change amount until the motor speed reaches the synchronous speed range.

[0040] In a specific example of the present application, the control system controls the opening angle of the blade to decrease uniformly by 5°.

[0041] In some other embodiments of the present application, the opening angle of the blade can also be reduced variably. For example, set the change amount of the opening angle according to the motor speed, and a curve graph can also be constructed based on the relationship between the opening angle of the blade and the motor speed, so as to determine the change amount of the opening angle according to the curve graph. Specifically, it includes: Based on the opening angle of the blade and the motor speed at different wind speeds, construct a curve graph of the motor speed changing with the opening angle of the blade at different wind speeds; Based on the curve graph of the motor speed changing with the opening angle of the blade corresponding to the current wind speed, obtain the target opening angle of the blade corresponding to the synchronous speed range; Based on the opening angle of the blade and the target opening angle, set the change amount of the opening angle, and control the opening angle of the blade to decrease by the change amount of the opening angle until the motor speed reaches the synchronous speed range.

[0042] An embodiment of the present application further provides a control system, which is used to implement the steps of the above-mentioned power reduction grid connection method for a wind turbine generator set.

[0043] It should be noted that the present application has designed a corresponding control system based on the above grid connection method. As Figure 3 shown in the entity diagram of the control system, this control system can be used for the manual / automatic parallel connection of a single wind turbine generator set with ten points, and at the same time, it can realize functions such as automatic startup / shutdown / parallel operation, data measurement, alarm protection, and "three remote" functions.

[0044] Those skilled in the art should understand that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the present application can take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present application can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0045] The present application is described with reference to the flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or block in the flowchart and / or block diagram can be implemented by computer program instructions, and the combination of processes and / or blocks in the flowchart and / or block diagram can also be implemented. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing devices generate a device for implementing the functions specified in Figure 1 one process or multiple processes and / or blocks Figure 1 one block or multiple blocks.

[0046] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer-readable memory generate a manufactured article including an instruction device, and the instruction device implements the functions specified in Figure 1 one process or multiple processes and / or blocks Figure 1 one block or multiple blocks.

[0047] These computer program instructions can also be loaded onto a computer or other programmable data processing device, so that a series of operation steps are executed on the computer or other programmable device to generate a computer-implemented process. Thus, the instructions executed on the computer or other programmable device provide for implementing the functions specified in Figure 1 one process or multiple processes and / or blocks Figure 1Steps of functions specified in one or more boxes.

[0048] Obviously, the above embodiments are only examples for clear illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A method for reducing power and connecting to the grid of a wind turbine generator set, characterized in that: Control systems used in wind turbines include: Monitor wind speed in real time. When the wind speed continuously meets the wind turbine operating wind speed within a preset period of time, calculate the output power of the wind turbine and determine the difference between the output power and the preset power threshold. If the output power is greater than the preset power threshold, the blade opening angle is controlled based on the current wind speed, thereby adjusting the motor speed; when the motor speed reaches the synchronous speed range, the motor is controlled to close and connect to the grid; Based on the real-time operating status parameters of the wind turbine, the real-time status parameters on the user side and the real-time status parameters on the grid side, the grid-connected status of the wind turbine is judged, and when the wind turbine fails to connect to the grid, the motor is controlled to trip and disconnect from the grid.

2. The method for reducing power and connecting to the grid of a wind turbine generator set according to claim 1, characterized in that: Based on the real-time operating status parameters of the wind turbine, the real-time status parameters of the user side and the real-time status parameters of the grid side, the grid-connected status of the wind turbine is judged. When the wind turbine fails to connect to the grid, the motor is controlled to trip and disconnect from the grid, including: Obtain the real-time output power of the wind turbine generator set, the real-time power consumption on the user side and the real-time output power on the grid side, and calculate the sum of the real-time output power of the wind turbine generator set and the real-time output power on the grid side; If the sum is not equal to the real-time power consumption on the user side, it is determined that the wind turbine generator set has a grid-connected failure and the motor is controlled to trip and disconnect from the grid.

3. The method for reducing power and connecting to the grid of a wind turbine generator set according to claim 1, characterized in that: Based on the real-time operating status parameters of the wind turbine, the real-time status parameters of the user side and the real-time status parameters of the grid side, the grid-connected status of the wind turbine is judged. When the wind turbine fails to connect to the grid, the motor is controlled to trip and disconnect from the grid, including: Determine whether the real-time output power of the wind turbine generator set is greater than the set ratio of the real-time power consumption on the user side; If the real-time output power of the wind turbine generator set is greater than the set proportion of the real-time power consumption on the user side, the wind turbine generator set is judged to have a grid-connected failure and the motor is controlled to trip and disconnect from the grid.

4. The method for reducing power and connecting to the grid of a wind turbine generator set according to claim 3, characterized in that: When the wind speed is less than or equal to 11m / s, the setting ratio is 80%; When the wind speed is greater than 11m / s and less than 13m / s, the setting ratio is 70%.

5. The method for reducing power and connecting to the grid of a wind turbine generator set according to claim 1, characterized in that: After controlling the motor to trip and disconnect from the grid, the method also includes: reducing the opening angle of the blades to adjust the motor speed, and when the motor speed reaches the synchronous speed range again, controlling the motor to close and connect to the grid.

6. The method for reducing power and connecting to the grid of a wind turbine generator set according to claim 5, characterized in that: Lowering the blade opening angle includes: controlling the blade opening angle to decrease at a constant speed with a fixed change amount until the motor speed reaches a synchronous speed range.

7. The method for reducing power and connecting to the grid of a wind turbine generator set according to claim 5, characterized in that: Reducing the blade opening angle includes: Based on the blade opening angle and motor speed under different wind speeds, a curve diagram of the motor speed changing with the blade opening angle under different wind speeds is constructed; Based on the curve diagram of the change of the motor speed corresponding to the current wind speed and the blade opening angle, the target blade opening angle corresponding to the synchronous speed range is obtained; Based on the blade's opening angle and the target opening angle, the opening angle change is set, and the blade's opening angle is controlled to decrease by the opening angle change until the motor speed reaches the synchronous speed range.

8. The method for reducing power and connecting to the grid of a wind turbine generator set according to claim 1, characterized in that: The preset time period is 10min~15min; and / or The wind turbine operates at a wind speed of 4m / s~25m / s; and / or The preset power threshold is 10Kw; and / or The synchronous speed range is 1490r / min~1510r / min.

9. The method for reducing power and connecting to the grid of a wind turbine generator set according to claim 1, characterized in that: The blade angles are controlled based on the current wind speed: When the wind speed is greater than or equal to 4m / s and less than or equal to 5m / s, the blade opening angle is controlled to be greater than 45° and less than 90°; When the wind speed is greater than 5m / s and less than or equal to 8m / s, the blade opening angle is controlled to be less than 45°.

10. A control system, characterized in that: The control system is used to implement the steps of the power reduction and grid-connection method for a wind turbine generator set as described in any one of claims 1 to 9.

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